There are numerous types of batteries with various advantages and disadvantages that depend on the battery application. Primary batteries, such as conventional alkaline batteries and primary metal-air batteries, operate through a single discharge cycle before the anode is exhausted and the battery must be replaced. Secondary batteries, such as lithium ion batteries, can be recharged and used through repeated charge/discharge cycles; however, the time period required for recharging the battery is often unacceptable in applications where a source of electricity is not readily available.
Fuel cells are similar to batteries, but can utilize hydrogen, methanol, formic acid, or other hydrocarbons as a fuel for the anode. Consequently, the fuel can be replenished indefinitely, eliminating the need for a long recharge step. However, wide-spread adoption of fuel cells has been hindered by the high cost of components required for operation. Typically, the air cathodes of a fuel cell utilize a high-cost platinum-based catalyst. Additionally, ionic membranes are required to separate the fuel and air, and these exotic membranes increase the cost and complexity of the fuel cell, its operation, and the manufacturability.
In addition to the high cost, fuel cell commercialization has been limited by the availability of hydrogen, and the difficulties with distributing and storing hydrogen. Direct methanol fuel cells (DMFCs) can operate using methanol and water as the fuel, providing a solution to the issues with hydrogen fuel. However, methanol can cross through the ionic electrolyte membrane, in a process known as “methanol crossover,” and directly oxidizes on the cathode, lowering the fuel cell voltage and power. Consequently, the concentration of methanol used as a fuel must be limited with conventional DMFCs to prevent methanol crossover. In turn, using less concentrated methanol solutions lowers the energy density of the fuel.